This invention relates to a transmission system in a working vehicle comprising a front housing and a transmission case which are arranged in series in a longitudinal direction of the vehicle and are fastened together. The front housing includes at its front end portion an engine flywheel, and the transmission case includes at least one speed change mechanism. In such a working vehicle, the present invention particularly relates to a transmission system in which two kinds of supplementary speed change mechanisms, which are connected in series, are provided in the front housing so as to effectively use the inside of the front housing.
In a working vehicle comprising a front housing, including at its front end portion an engine flywheel, and a transmission case, including at least one speed change mechanism, which are arranged in series and are fastened together, it is well known from, for example, U.S. Pat. No. 5,058,455 and No. 5,617,936 that a supplementary speed change mechanism such as a direction-reversing mechanism or high/low speed-selecting mechanism is provided in the front housing. However, it has not been known yet that two kinds of such supplementary speed change mechanisms which are connected in series are provided in the front housing.
However, it would be very advantageous if such two kinds of supplementary speed change mechanisms could be provided in the front housing in a simple structure without enlarging substantially the length of the front housing. In such a case, a variety of speed change transmissions could be offered without any substantial change in the speed change mechanism in the transmission case by omitting any one of the supplementary speed change mechanisms in the front housing.
Accordingly, a primary object of the present invention is to provide a novel transmission system in which two kinds of supplementary speed change mechanisms, namely a direction-revesing mechanism and a high/low speed-selecting mechanism which are connected in series, are provided in a front housing of a working vehicle.
An attendant object of the invention is to provide a transmission system which is easy in assembly notwithstanding the provision of two kinds of supplementary speed change mechanisms.
Another attendant object is to provide a transmission system which is simple in structure and which does not lengthen the front housing.
The present invention relates to a transmission system in a working vehicle comprising a front housing (1), including at its front end portion an engine flywheel (6), and a transmission case (2), including at least one speed change mechanism (17, 20), which are arranged in series in a longitudinal direction of the vehicle and are fastened together. The transmission system according to the present invention is characterized in:
that there are provided in the front housing (1) a primary drive shaft (8) which is co-axial with the engine flywheel (6) and is adapted to be driven to rotate by the engine flywheel, a transmission shaft (11) which is arranged in parallel with the primary drive shaft, and an output shaft (13) which is co-axial with the primary drive shaft, the output shaft (13) being connected to the speed change mechanism (17, 20); and
that a first two-ratio supplementary speed change mechanism (12) is disposed between the primary drive shaft (8) and the transmission shaft (11) and a second two-ratio supplementary speed change mechanism (14) is disposed between the transmission shaft (11) and the output shaft (13), one of the first and second supplementary speed change mechanism (12) being formed into a direction-reversing mechanism and the other of the first and second supplementary speed change mechanism (14) being formed into a high/low speed-selecting mechanism.
The primary drive shaft (8), provided in the front housing (1) such that it is co-axial with the engine flywheel (6), can be connected to the flywheel in a simplest manner. Because the primary drive shaft (8) and the output shaft (13) are arranged co-axially with each other, a rear end portion of the primary drive shaft and a front end portion of the output shaft can be supported by a single bearing support bore which is formed in and through a common bearing support wall. The first two-ratio supplementary speed change mechanism (12) and the second two-ratio supplementary speed change mechanism (14) are connected in series to each other by the transmission shaft (11) which is commonly employed for providing the first and second supplementary speed change mechanisms (12, 14), so that two kinds of supplementary speed change mechanisms which are connected in series are provided by employing a minimum number of the three shafts (8, 11, 13). Consequently, two kinds of the supplementary speed change mechanisms are provided in the front housing without any substantial enlargement of the housing. A variety of speed change transmissions can be offered without any substantial change in the speed change mechanism (17, 20) in the transmission case (2) by connecting between the primary drive shaft and the transmission shaft or between the transmission shaft and the output shaft through meshing gears in place of the first or second supplementary speed change mechanism.
For facilitating the assembly, it is preferred that the front housing (1) includes a first bearing support wall (1a) disposed before the first supplementary speed change mechanism (12) and a second bearing support wall (4) disposed between the first and second supplementary speed change mechanisms (12, 14), and that a third bearing support wall (5) disposed behind the second supplementary speed change mechanism (14) is provided at a location adjacent to a rear end of the front housing (1), the second bearing support wall (4) being removably secured to the front housing (1) and the third bearing support wall (5) being removably secured to the front housing (1) or to the transmission case (2). According to this structure, the first supplemetary speed change mechanism (12) can be assembled into the front housing (1) from the rear end thereof using the removable second bearing support wall (4) as a support therefor and, then, the second supplementary speed change mechanism (14) can be assembled into the front housing (1) from the rear end thereof using the removable third bearing support wall (5) as a support therefor.
The second supplementary speed change mechanism (14) can be formed into an easily operable fluid-operated type in which two clutches (45, 46) which are selectively supplied with fluid pressure for performing two-ratio speed change transmissin are mounted on the transmission shaft (11). In this case, it is preferred that the transmission shaft (11) includes at least one fluid passage (61) for supplying operating fluid to the clutches (45, 46) and a lubricant passage (69) for supplying lubricant to the clutches (45, 46), a rotary joint (65) for connecting the fluid passage (61) to a stationary fluid passage (67) being formed within the second bearing support wall (4) and another rotary joint (70) for connecting the lubricant passage (69) to a stationary lubricant passage (73) being formed within the first bearing support wall (1a). According to this structure, the rotary joint (65) for the fluid passage in the transmission shaft and the rotary joint (70) for the lubricant passage in the transmission shaft are formed at locations spaced from each other in a longitudinal direction of the transmission shaft so that the thickness of each of the first and second bearing support walls (1a, 4) can be made as small as possible, whereby enlargement of the length of the front housing (1) can be avoided.
More preferably, one of the clutches (45) is formed into a fluid-actuated frictional clutch having a first set of frictional elements (47, 48), a first piston (49) for engaging between the first set of frictional elements under the action of fluid pressure, and a return spring (50) for biasing the first piston to move away from the first set of frictional elements so as to disengage between the first set of frictional elements, whereas the other of the clutches (46) is formed into a spring-actuated frictional clutch having a second set of frictional elements (52, 53), a spring (56) for engaging between the second set of frictional elements, and a second piston (59) for disactuating the spring under the action of fluid pressure so as to disengage between the second set of frictional elements, said at least one fluid passage (61) in the transmission shaft (11) being composed of a single fluid passage through which fluid pressure is selectively supplied to and drained from the first and second pistons (49, 59) for performing the speed change transmission by the second supplementary speed change mechanism (14). According to this structure, when a trouble is caused in the fluid supply system for the second supplementary speed change mechanism the spring-actuated frictional clutch (46) will be automatically engaged due to the loss of fluid pressure applied to the second piston (59). Consequently, the vehicle drive line is not cut off at the second supplementary speed change mechanism, so that an engine brake action can be achieved. Because the fluid passage in the transmission shaft is a single one (61) and the single rotary joint (65) for such a single passage is satisfactory, the fluid passage structure for the second supplementary speed change mechanism is very simple. The length of the transmission shaft (11) can be small so that enlargement of the length of the front housing is avoided, too.
For simlifying the structure of the second supplementary speed change mechanism, it is preferred that a clutch cylinder (44) having a partition (44a) at an axially middle portion thereof is fixedly mounted on the transmission shaft (11), that the one clutch (45) is disposed within one axial half of the clutch cylinder (44) with the first piston (49) being disposed at a location adjacent to the partition (44a), and that the other clutch (46) is disposed within the other axial half of the clutch cylinder (44) with the second set of frictional elements (52, 53) being disposed at a location adjacent to the partition (44a), the spring (56) being disposed such that it acts upon the second set of frictional elements through a push disk (54) which is slidably but non-rotatably supported by the clutch cylinder, the clutch cylinder (44) having an integral cylinder portion (58) at an outer circumference of the partition (44a) for receiving the second piston (59) such that the second piston abuts at an extension (59a) thereof against the push disk (54). According to this structure, the clutch cylinder (44) is commonly employed for both of the clutches (45, 46). The structure that the clyinder portion (58) for receiving the second piston (59) is formed integrally with the clutch cylinder is simple, and the structure of the other clutch (46) is reasonable as a spring-actuated type.
For simplifying fluid passage structure in the clutch cylinder (44), it is preferred that the clutch cylinder (44) includes a fluid passage (62) for connecting the fluid passage (61) in the transmission shaft (11) to a fluid chamber (51) which is formed between the first piston (49) and the partition (44a), and another fluid passage (63) for connecting the fluid chamber (51) to a fluid chamber (60) in the cylinder portion (58). According to this structure, the former fluid chamber (51) acts as a fluid chamber for operating the first piston (49) and the latter fluid chamber (60) acts as a fluid chamber for operating the second piston (59). The fluid chamber (60) for operating the second piston (59) is supplied and drained with fluid pressure through the another fluid passage (63) and through the fluid chamber (60), so that the fluid passage structure in the clutch cylinder is simplified.
For shortening the clutch structure of the second supplementary speed change mechanism, it is preferred that the first piston (49) and the second piston (59) are partially overlapped in an axial direction of the clutch cylinder (44). According to this structure, the stroke of the first piston (49) and the stroke of the second piston (59) are partially overlapped in an axial direction of the clutch cylinder so that the clutch structure of the second supplementary speed change mechanism is shortened.
The present invention also relates to a speed change mechanism in a working vehicle which comprises two gears (40, 41) rotatably mounted on a transmission shaft (11) and two frictional clutches (45, 46) mounted on the transmission shaft for coupling the gears one at a time to the transmission shaft so as to perform a two-ratio speed change transmission. The speed change mechanism according to the present invention is characterized in:
that one of the clutches (45) is formed into a fluid-actuated clutch which is actuated by an engagement between a first set of frictional elements (47, 48) under the action of fluid pressure applied to a first piston (49) and which is disactuated by the force of a return spring (50) acting upon the first piston, whereas the other of the clutches (46) is formed into a spring-actuated clutch which is actuated by an engagement of a second set of frictional elements (52, 53) under the action of a spring (56) and which is disactuated under the action of fluid pressure applied to a second piston (59), and
that the transmission shaft (11) includes a single operating fluid passage (61) for supplying fluid to the first piston (49) and to the second piston (59), fluid pressure being applied to and drained from the first and second pistons respectively at a same time through the fluid passage so as to perform the two-ratio speed change transmission.
According to this structure, when a trouble is caused in the fluid supply system for the speed change mechanism the spring-actuated frictional clutch (46) will be automatically engaged due to the loss of fluid pressure applied to the second piston (59). Consequently, the vehicle drive line is not cut off at the speed change mechanism, so that an engine brake action can be achieved. Because the fluid passage in the transmission shaft is a single one (61) and the single rotary joint (65) for such a single passage is satisfactory, the fluid passage structure for the speed change mechanism is very simple and the length of the transmission shaft (11) can be small.